Numerous therapies have been developed to address the needs of individuals suffering from heart diseases or abnormalities. For a first example, individuals suffering from bradycardia, or an abnormally slow heart rate, can be treated using a pacemaker. A pacemaker alters the individual's heart rate to return heart rate performance to normal levels. A pacemaker typically accomplishes this by delivering a series of electrical impulses to the heart tissue via one or more leads, thereby stimulating the heart tissue to contract at a specified rate. Therefore, a primary function of bradycardia therapy using a pacemaker is to provide rate support for the heart.
The pacemaker typically functions as an on-demand device, meaning that the pacemaker will function only when rate support is necessary. The pacemaker will typically delay for a certain duration, termed an escape interval, before providing an electrical impulse to the heart. If the intrinsic electrical activity of the individual's heart causes the heart to contract before the escape interval expires, the pacemaker will not send an electrical impulse. Instead, the pacemaker will reset the escape interval and wait for the escape interval to expire again. Therefore, if the individual's heart is beating at a specified acceptable rate, the pacemaker will not provide an electrical impulse until rate support is needed. Other functions of a pacemaker may include adaptive-rate pacing, in which the rate of the pacing is increased or decreased based on an individual's physiological needs.
In a second example of a heart abnormality, individuals may exhibit a decrease in hemodynamic efficiency due to the onset of congestive heart failure (CHF). A possible therapy for CHF is the use of a cardiac resynchronization therapy (CRT) device. A CRT device, like a pacemaker, can deliver a series of electrical impulses to a heart tissue. However, a CRT device functions to synchronize the contraction of a heart rather than to pace the heart like a pacemaker. A CRT device may deliver a series of electrical impulses to the heart at a set rate, usually in conjunction with each intrinsic heartbeat, to synchronize the contraction of different sections of the heart. Research and development into the use of a CRT device to treat CHF has established a set of therapeutic features that can be customized for each individual in order to maximize hemodynamic function. For instance, methods have been developed for optimizing the timing between electrical stimuli, thereby providing maximum resynchronization benefits. Therefore, a primary function of a CRT device is resynchronization, making the timing and the delivery of each electrical impulse for each heartbeat important.
Consequently, while bradycardia therapy focuses on rate support on an as-needed basis, CHF therapy focuses on resynchronization. During resynchronization, particular attention may be paid to atrioventricular delays, and electrical impulses are typically provided for every heartbeat. Because therapeutic priorities of bradycardia patients differ from those of CHF patients, it is a current practice in the industry to design different products for a patient depending on whether a patient exhibits bradycardia or CHF. Therefore, initial decisions must be made for each patient on whether to implant a bradycardia pacemaker or a CHF cardiac resynchronization therapy device.
Currently, pacemakers and CRT devices are not interchangeable, and a pacemaker cannot be reprogrammed to be a CRT device and vice versa. Therefore, not only must treatment decisions be made initially, once a device is implanted into the patient, it cannot be adapted should the patient's needs change, such as, for example, from a need for bradycardia therapy to a need for cardiac resynchronization therapy. Further, product development costs are increased because separate devices must be designed.
It would therefore be desirable to develop a cardiac rhythm management system having multiple therapy modalities.